Cervical dilation measuring device

ABSTRACT

A measuring device for measuring cervix dilation is disclosed. The device comprises a miniature signal transmitting device attached to one side of the cervix, said transmitting device generating a signal whose intensity varies with the distance from said transmitting device. A miniature receiving device attached to or placed against an opposite side of the cervix from said transmitting device receives the transmitted signal and generates a signal proportional to said transmitted signal. The signal from said receiving device is passed through translation means to provide a visible display of the intensity of said transmitted signal. The intensity of said transmitted signal is proportional to the distance between the transmitting device and the receiving device.

United States Patent [1 1 Cannon et al.

[ 1 Oct. 30, 1973 Hehertson, both of Salt Lake City, Utah [73] Assignee:Utah Research & Development Co.,

Inc., Salt Lake City, Utah [22] Filed: June 28, 1971 [21] Appl. No.:157,154

4/1969 Salmons 128/2 S 9/1971 Estes 128/2 S Primary Examiner-William E.Kamm Attorney-William S. Britt et a1.

[57] ABSTRACT A measuring device for measuring cervix dilation isdisclosed. The device comprises a miniature signal transmitting deviceattached to one side of the cervix, said transmitting device generatinga signal whose intensity varies with the distance from said transmittingdevice. A miniature receiving device attached to or placed against anopposite side of the cervix from said transmitting device receives thetransmitted signal and generates a signal proportional to saidtransmitted signal. The signal from said receiving device is passedthrough translation means to provide a visible display of the intensityof said transmitted signal. The intensity of said transmitted signal isproportional to the distance between the transmitting device and thereceiving device.

10 Claims, 7 Drawing Figures L 0171700176 1 COIL A COIL B [52] US. Cl.128/2 S, 340/248, 340/282 Field of Search 128/2 R, 2 S, 2.1 R, 128/2.05R, 1.3, 1.5; 33/174 D; 340/248, 279, 282

[56] References Cited UNITED STATES PATENTS 3,273,559 9/1966 Evans 128/2S 3,526,886 9/1970 Lubich 340/282 3,547,106 12/1970 Bommann... 128/2 R2,393,717 l/1946 Speaker l28/l.5

SIGNAL GENERATOR PEAK FOLLOWER LOG AMPLIFIER ANTI-LOG AMPLIFIER VISUALDISPLAY PATENTEDHCI 30 I975.

SHEET 1 [IF 3 SIGNAL GENERATOR (ma/r1000 l COIL A u euoueee 1 B PEAKFoLLowER LOG AMPLIFIER ANTI-LOG AMPLIFIER VISUAL DISPLAY D.C. PowERSUPPLY D.C./A.C. CONVERTER OSCILLATOR MM L uuuv I TRANSMITTING COILPowER SUPPLY IIIIIIII RECEIVING COIL REcEIvER TRANSMITTER AMPLIFIER igLOG ANTI-LOG VISUAL P IFI MP IFI R DI PLAY FoLLowER AM L ER A L E sINVENTORS EMERSON T. CANNON RICHARD M. HEBERTSOP AT TORNE Y PATENTED URI3 0' I975 SHEET 2 BF 3 D. C. POWER SUPPLY 0. c. TO A. c. CONVERTER D. c.I

' MINATURE MlNATURE CONVERTER TRANSMITTER x TRANSMITTER Y REMOTE RECEWERINVENTORS EMERSON T CANNON RICHARD M. HEBERTSON PATENTEnnm 30 m3 SHEET 3BF 3 TIME F /G. 6

TIME F/G. 7.

ATTORNEY CERVICAL DILATION MEASURING DEVICE BACKGROUND OF THEINVENTION 1. Field Frequent measurement of cervical dilation is requiredupon a prospective mother during the period immediately prior tochildbirth. Present means for physically measuring the distance betweencervical walls adds to the discomfort of the patient and requiresfrequent attention of medical personnel. Means of remotely measuring orat least remotely displaying a periodically or continuously monitoredmeasurement of cervix dilation is desired.

Prior Art No prior art technique for applying electrical or electronicmeans to measuring cervix dilation is known to applicant. The followingpatents describe electrical or electronic means generally for measuringdistances.

U.S. Pat. No. 3,387,496 of Cornelius describes an apparatus formeasuring extremely small distances, for example, one-one millionth of amillimeter. The apparatus of Cornelius utilizes variation in inductanceor capacitance caused by physical changes in an LRC circuit, resultingin a change in the frequency at which said LRC circuit oscillates,thereby indicating the distance measured. The distance may be measuredby varying the distance between the plates of a capacitor and measuringthe new capacitance. The change in capacitance changes the frequency atwhich the circuit oscillates. Also, a pair of coils are utilized inwhich a change in inductance is caused by movement of the core within acoil.

U.S. Pat. No. 2,369,909 of Mestas describes a device for measuring theinternal diameter of tubes and the like wherein a primary coil and twosecondary coils are physically aligned and contained within acylindrical structure. An elongated armature, pivoted at one end, swingsthrough a very short arc at the free end, thereby causing unequal airgaps to exist between said armature and said secondary coils, resultingin current flow in an ordinarily balanced circuit.

Another patent of interest is U.S. Pat. No. 2,736,967 of Doll wherein anelectrical means is disclosed for measuring the diameter of undergroundshafts. A transmitting coil or rotating magnet and receiving coil aremade part of a' well-logging and caliper device transported through aborehole. The caliper portion of the device comprises one coil attachedto spring-like members in contact with the borehole wall and anothercoil located in a central member of the caliper device. Variation of thedistance between coils causes a change in intensityv of current inducedin one of the coils thereby providing a signal proportional to theborehole diameter.

OBJECTS OF THE INVENTION To provide means for substantially constantlymeasuring cervical dilation.

To provide means for attaching to the cervix a transmitting device and areceiving device whereby an electromagnetic signal is transmitted whosecharacter at the receiving device is dependent upon the degree ofcervical dilation.

To provide means for remotely displaying the degree of cervix dilationpresent in a prospective mother at any given moment.

To provide means for recording the degree of cervical dilation presentin a prospective mother.

To provide a cervix measuring device wherein at least a portion of thecomponents thereof are physically attached to the cervix near itsopening and which are substantially unaffected by body fluids.

To provide a cervix measuring device which causes substantially no riskor harm to a prospective mother or fetus.

To provide a cervix measuring device wherein the accuracy of measurementis greater than about percent.

DESCRIPTION OF THE INVENTION A measuring apparatus for periodically orcontinuously measuring cervical dilation of a prospective mother has nowbeen invented. The apparatus comprises at least one miniature signaltransmitting device attached to the cervical wall which transmits anelectromagnetic signal, a signal receiving device for receiving saidtransmitted signal wherein the character of said signal correlates withthe diameter of the cervical opening and display means interacting withsaid receiving means to display the received signal in a manner whichindicates cervical dilation.

Further understanding of the invention may be facilitated by referenceto the accompanying drawings.

FIG. 1 is a block diagram of a cervix measuring device utilizing atransmitting coil and a receiving coil.

FIG. 2 is a perspective view of an encapsulated coil for attachment to acervix wall.

FIG. 3 is a block diagram of a cervix measuring device utilizing aself-contained transmitting-receiving coil system which transmits adistance-proportional signal to a remote receiver.

FIG. 4 is a perspective view of a cervix measuring probe and permanentmagnet transmitters.

FIG. 5 is a block diagram of a cervix measuring device wherein a pair oftransmitting devices attached to opposite cervix walls transmit signalsof different frequencies to a remote receiver.

FIG. 6 is a chart typifying a continuous plot of cervical dilationdistance against time.

FIG. 7 is a chart typifying a periodic plot of cervical dilationdistance against time.

A preferred embodiment of the invention is illustrated in FIG. 1. Asignal generator supplies an alternating current having low voltage,generally less than about 25 volts and preferably less than about 10volts, and very low power, generally less than milliwatts and preferablyless than 50 milliwatts, to a transmitting coil, Coil A. The frequencyof the current supplied to Coil A depends, at least partly, upon theproperties of Coil A. The frequency of the alternating current suppliedto Coil A preferably matches the resonant frequency of the coil or atleast falls within the band-pass of the coil.

The alternating current passing through Coil A induces an alternatingcurrent in Coil B. The voltage of the current produced in Coil B dependsupon the amount of voltage impressed upon Coil A, the frequency of thecurrent in Coil A, the characteristics of Coil A and Coil B, and thedistance between Coil A and Coil B. The voltage produced in Coil B isinversely proportional to the cube of the distance between Coils A andB. Therefore, the voltage produced in Coil B for a given impressedvoltage, frequency and coil characteristics will be 6 as great at aspacing of two centimeters between the coils as occurs with a spacing ofone centimeter.

The induced voltage in Coil B is an alternating current of potentiallythe same frequency as that impressed upon Coil A. The alternatingcurrent from Coil B is passed through a peak follower which measures themaximum voltage in each cycle and produces a direct current whichcorresponds to the peak voltage of the alternating current. Anexponential relationship between distance and voltage still exists. Thedirect current from the peak follower is passed through a log amplifierwhich amplifies the voltage. Although the distance between Coils A and Bcould be determined by using a log graph and charting the voltagereadings from the log amplifier thereon it is preferred to pass theamplified direct current to an anti-log amplifier which takes theanti-log of the input voltage and establishes a linear relationshipbetween the voltage and distance existing between Coils A and B. Thecurrent from the anti-log amplifier can be passed into a visual displaydevice wherein the distance may be represented digitally or graphicallyto provide a continuous chart of the various distances existing betweenCoil A and Coil B over a given period of time. Oscilliscopes, digitalread-out devices, recorders and the like are useful display devices.

The signal generator of FIG. 1 may be a conventional signal generatorfor generating alternating currents of frequencies from about 50kilocycles per second to about 1000 kilocycles per second (KCS) althoughit is generally preferred to use frequencies less than about 550 KCS sothat interference by commercial radio transmissions will not occur.Inasmuch as a portion of the device comprises an encapsulated coil incontact with a humanpatient, it is preferred that ultra high frequenciesbe avoided and that voltages of less than 25 volts at low power levels,i.e. below 50 milliwatts be utilized.

The signal generator preferably operates on 1 10 volts input, however, atransformer cannot be used to transform 1 10 volts to the low voltagedesired inasmuch as the power level would be excessive. Direct currentfrom a dry cell producing to volts or more can be passed through anoscillator or other direct current to alternating current converter foruse in devices of this invention.

The peak follower, log amplifiter, anti-log amplifier and visual displaycomponents are commercially available items or items which can beconstructed of conventional design.

Coils A and B are preferably identical in size and construction. Thecoils are preferably encapsulated in a resinous substance to protect thecoils from body fluids. The encapsulating material, of course, shouldnot interfere with the electro-magnetic properties of the coil. Thecoils are preferably attached to the cervix by clamps or otherappropriate means, see FIG. 2, and are preferably small in size. Themaximum dimension of a coil consistant with comfort to the patient isabout '15 inch and a maximum dimension of :4 inch is preferred. Becauseof the size limitations a small core and fine wire must be utilized informing the coils.

One preferred coil construction comprises a small ferrite core havingdimensions of about 1.75 millimeters by two millimeters by fivemillimeters wherein about 200 turns of number 39 wire is takenthereabout.

The resonant frequency of coils of this construction is between about350 and 400 KCS. It is preferred, generally, that both coils of thesystem of FIG. 1 have substantially the same construction, that is,identical core size, core material and an identical number of turns ofthe same type and size of wire.

Although the dimensions of the core, core material, size of wire andnumber of turns of wire on the coil can be varied substantially fromthat described above, it is preferred that the coil be constructed tohave maximum inductance for its size. It is further preferred that eachcoil be identical in construction so that each will operate at the sameresonant frequency and therefore provide greatest efficiency ofoperation. Maximum efficiency is preferred inasmuch as it is verydesirable to operate the system at low power and low voltage to minimizeany potential danger to the patient or fetus.

A ferrite core is preferred and it is generally preferred that at leastabout turns be present on each coil. The inductance of the coil may beincreased by increasing the number of turns and/or increasing thecross-sectional area of the core and/or decreasing the length of thecore. The resonant frequency of the coil is inversely proportional tothe square root of the inductance. Therefore, those things whichincrease the inductance generally lower the resonant frequency. Besidesimproving the efficiency of the system, operation at resonant frequencyeliminates the necessity of calibrating the measuring device each timeit is used. The inductance of coils useful in this invention may be anyconvenient value and may be varied over a very broad range.

When a voltage of 10 volts at 350 to 400 KCS is applied to Coil A havingthe construction described hereinabove, a voltage of 1 millivolt in CoilB is induced at a distance of about 16 centimeters. inasmuch as theinduced voltage is inversely proportional to the cube of the distancebetween Coils A and B, under these conditions an induced voltage of 8millivolts would occur in Coil B at a distance of 8 centimeters. Thevoltage induced in Coil B can be proportionately increased by increasingthe voltage applied to Coil A. Under the same conditions of frequency, a2 millivolt induced voltage would occur in Coil B when 20 volts areapplied to Coil A.

An accuracy of about one-quarter centimeter is preferred for themeasuring device of this invention. Using commercial components orcomponents of conventional design, an accuracy of plus or minus onemillivolt is easily attained. Therefore, for each one centimeter, avoltage differential of at least four millivolts is desired.

The coils utilized in this invention frequently are high Q devicesinasmuch as the resistance of the coil is low in relation to itsinductance. Such coils, therefore, have a narrow frequency bandpass.However, a broader band-pass coil can be obtained by artificiallyintroducing greater resistance into the circuit. This increases thepower required. Although a broad band-pass coil is advantageous, asubstantial increase in power beyond a 100 millivolt limit in a cervicalmeasuring device is undesirable.

A pair of coils in the system of FIG. 1 is required for each patient.However, a plurality of patients can be served by utilizing a pluralityof pairs of coils, each pair constructed to operate at a differentresonant frequency. Through use of a switching device and a variablefrequency signal operator, more than one patient could be served withoutduplication of translation components. A periodic reading for eachfrequency could be provided.

The coil shown in FIG. 2 is typical of those useful in this invention.As indicated hereinabove, the maximum dimension in any direction shouldnot exceed one-half inch while a maximum, dimension of not greater thanabout one-quarter inch is preferred. The coil illustrated has acylindrical body 11 with a pair of opposed clamps which may be used forattaching the coil to flesh in the cervix region. A single arrow-shapedbarb is another convenient way of attaching each coil to the patient.The coil may be of any desired shape, although a square or round coreprovides the greatest crosssectional area consistent with smalldimensions. A thin, flat coil has some advantage, however, in that itcan be placed in the cervical region without unduly projecting from thetissue to which it is attached.

As indicated hereinabove, the coils forming part of the measuring deviceof this invention are encapsulated in a resinous or other material whichdoes not interfere with the electro-magnetic field being generated andwhich protects the coil from contact with body fluids. Very fine wirehaving very thin insulation is used in winding coils. The thin wire andinsulation thereon renders the coils subject to being easily damaged.The coils must be encapsulated (potted) to protect the fine wire frombreakage and from being shorted through contact of body fluids. Also,the fine wires are easily broken and are protected from physical damageby the encapsulating material.

During encapsulation, care must be taken to avoid elevated temperaturesinasmuch as this destroys the insulation on the wires. Also, extremepressures cannot be used to mold resinous material about the coilsbecause of the fragile nature of the wire involved. Preferredencapsulating materials are room-temperature curing materials orthermoplastic materials which can be easily molded at temperatures lessthan about 250F. Room-temperature curing polysilicone resins have beenfound useful for this purpose. The resins used for encapsulation ofcoils should be substantially moisture impermeable, resistant to alcoholor ether sterilization and be formable or curable at sufficiently lowtemperatures to avoid removing the insulation from the fine wires in thecoil. Thermoplastic resins such as polystyrene and polyvinylidenechloride (Saran) are useful while thermosetting resins which cure atroom temperature such as polysiloxanes and polybutenes can be used.Temperature limitations of the encapsulating resin are dependent uponthe wire coating, therefore, if temperature-resistant wire coatings areused higher temperature curing resins can be utilized.

In FIG. 3 a slightly different arrangement is illustrated for the cervixmeasuring device. A D. C. power supply, such as a miniature dry cell,supplies current to a D.C./A.C. converter such as an oscillator whichsupplies alternating current of a desired frequency to the transmittingcoil. The voltage induced in the receiving coil is transmitted to areceiver and further transmitted to an amplifier which is also poweredby miniature power supply. The amplified, induced signal is fed to atransmitter which then transmits an electromagnetic wave proportional inintensity to the signal received from the receiving coil. The amplified,transmitted signal is received by a remote receiver and fed to a peakfollower and ultimately into a log amplifier, antilog amplifier andvisual display device. An advantage of this system provides a powersupply, a converter for the transmitting coil and a power supply,amplifier and receiver and transmitter for the receiving coil which allcan be attached to the patient or in the vicinity of the patient withoutrequiring leads to be run from the patient to the peak follower andassociated components.

In FIG. 4 a cervix measuring device utilizing one or a pair of permanentmagnets is illustrated. The apparatus illustrated in FIG. 4 performseffectively when a single permanent magnet 12 is utilized and the probe13 is placed against the opposite cervix wall. The probe 13 comprises aplastic, tubular outer-shell 14 containing a coil I5 which is vibratedat a substantially constant rate so that a voltage is induced in thecoil when it is placed in the presence of a magnetic field. The coil 15is preferably wound upon a core 16 which may be vibrated mechanicallysuch as contacting an eccentric wheel 17 rotated through a flexiblecoupling 18 by a remote motor. The core 16 may be spring-loaded or incontact with resilient filler 19 at the end of the core opposite theeccentric wheel 17.

The coil 15 should preferably be reciprocated at a relatively fast rateso that a slight movement of the probe during the recording of thevoltage would not substantially interfere or lead to an erroneousreading.

The voltage induced in the vibrating coil I5 of probe 13 will bedependent upon the reciprocating frequency of the coil and the fluxdensity of the permanent magnet. If the flux density of the magnet andthe reciprocating frequency of the coil are each substantially constant,then the induced voltage in coil 15 is dependent upon the distancebetween the permanent magnet and the coil. It is necessary, therefore,to replace the probe in substantially the same position on the cervixwall opposite from the permanent magnet for each succeeding measurement.

The advantage of this system resides in its simplicity and lack ofconnecting wires and components attached to the patient. The onlycomponent attached to the patient is a small permanent magnet which issecured to the tissue adjacent one cervix wall. No other components areattached to the patient and remote recording device. Another advantageof this device is that the device may be used substantially concurrentlywith a number of patients.

The voltage induced in coil 15 is preferably passed through a peakfollower and amplification and display system of the type illustrated inFIG. 1. The system illustrated in FIG. 4 is advantageous inasmuch asbody fluids and other environmental factors do not affect the fluxgenerated by the permanent magnet. The permanent magnet need not beencapsulated. The flux density may be increased by attaching two or morepermanent magnets adjacently to one wall of the cervix.

The measuring device illustrated in FIG. 5 utilizes a pair of miniaturetransmitters X and Y wherein the frequency of the signal transmitted isdifferent for each transmitter. The system is illustrated as having aD.C. power supply feeding D.C. to A.C. converter which powers theminiature transmitter which may, of course, be a coil similar to thecoils described in reference to FIGS. 1 and 2 whereby each transmitteroperates on a substantially different frequency. A remote receiverreceives the signals transmitted by both transmitter X and Y. Theinterference frequency generated by transmitters X and Y will change asthe distance changes between transmitters X and Y. The remote receiveris calibrated to determine the distance existing between X and Ydepending upon the interference of the frequency received. TransmittersX and Y are attached to opposite walls of the cervix and it is preferredthat the remote receiver be placed in a stationary position with regardto the patient. Also, a probe of the type described in FIG. 4 can beutilized within the cervical opening to determine the interferencefrequency. A probe utilized with a system such as that illustrated inFIG. 5 does not have to have an oscillating or vibrating coil inasmuchas the signals generated by transmitters X and Y would be alternating innature.

FIGS. 6 and 7 show one type of visual display which may be produced bythe measuring device of this invention. FIG. 6 illustrates a continuouschart in which dilation distance is plotted against time. A continuousrecording chart can be utilized for this purpose as part of the visualdisplay mentioned in regard to FIGS. 1, 3 and 5. A continuous plot ofthe cervical opening against time can be recorded and visually observedperiodically by medical attendants. In connection with such a display,an audible signal can be actuated whenever the chart indicates that acertain predetermined cervix opening had been reached. Also, acontinuous recording of the cervix opening makes changes in the rate ofcervical dilation visually observable, as shown by the change in slopeof the line in FIG. 6, designated by the length S. A continuousmeasurement and continuous recording provides maximum monitoring of thepatient and provides the medical attendant with the maximum ofinformation on the progress of dilation. Also, should dilationprematurely terminate the visual display would render this fact readilydiscernable, as shown in FIG. 6. By having several displays locatedcentrally, a single medical attendant could monitor the progress of oneor more patients efficiently.

A continuous chart of the type illustrated in FIGS. 6 providesdiagnostic and historical information on childbirth characteristics foreach mother. Also, such a record may be utilized to determine if thereis any correlation between certain types of birth defects and theduration or type of labor involved.

Another type of visual display or chart is illustrated in FIGS. 7. Thistype of display results from any of the above types of measuring devicesdescribed wherein a signal is generated only periodically or a periodicmeasurement is taken by use of a probe such as that described in FIG. 4.This type of chart also provides a continuous record with some intervalbetween individual measurements.

The cervix measuring devices of this invention are characterized by lowvoltage operation, i.e. 25 volts and preferably less than 10 volts; lackof physical connections between a signal transmitting device and asignal receiving device; signal frequencies of between about 50 and 1000KCS and preferably between 100 and 500 KCS. 7

Although the instant invention has been described hereinabove byreference to specific embodiments, it is not intended to be limitedthereto but to include all the variations and modifications fallingwithin the scope of the appended claims.

We claim:

1. An electromagnetic device for measuring cervical dilation comprising:

a. a first miniature induction coil having a resonant frequency betweenabout 50 and 1000 KCS, said first coil having means to attach said coilto the cervix of a prospective mother,

b. a second miniature coil having a resonant frequency substantially thesame as said first coil, said second having means to attach said coil tothe cervix of a prospective mother,

c. calibrated power supply means producing an oscillating current of afrequency substantially matching the resonant frequency of said firstminiature induction coil connected to said first miniature inductioncoil to provide predetermined amounts of induced energy in said secondcoil at predetermined distances from said first coil,

d. translation means interconnected with said second coil to translatethe intensity of voltage induced in said coil into a visible displaylinearly proportional to the distance separating said first and secondcoils.

2. The measuring device of claim 1 wherein the power supply meansprovides a low voltage, alternating current.

3. The measuring device of claim 2 wherein the power supply meansprovides an alternating current of less than about 25 volts.

4. The measuring device of claim 2 wherein the power supply meansprovides an alternating current of less than about milliwatts.

5. The measuring device of claim 1 wherein said translation meanscomprises a peak follower interconnected with said second coil, a logamplifier interconnected with said peak follower, an anti-log amplifierinterconnected with said log amplifier and a visual display device forconverting an electrical signal into a visual display.

6. The measuring device of claim 1 wherein the induction coils have ahigh Q and a narrow frequency band pass.

7. The measuring device of claim 6 wherein the power supply meansprovides an oscillating current at a power of less than about 100milliwatts, a voltage of less than about 25 volts and at a frequencywithin the band pass range of said coils.

8. The measuring device of claim 1 wherein each induction coil has amaximum dimension of about onehalf inch.

9. A measuring device for measuring cervical dilation comprising:

a. first miniature signal transmitting device having attachment means sosaid device can be attached to one side of the cervix, said transmittingdevice generating a signal of a substantially constant frequency.

b. a second miniature signal transmitting device having attachment meansso said device can be attached to the opposite side of said cervix fromsaid first transmitting device, said second transmitting devicegenerating a signal which has a substantially constant frequencydifferent from the frequency of the first transmitting device;

0. a remote receiving unit which receives an interference frequencytransmitted from said transmitting device;

(I. translation means for receiving said interference frequency fromsaid receiving device and translating same to provide a visible displayof the interference frequency received by the receiving device, saidtranslation means including a visual display device calibrated todisplay said interference frequency proportionally to the distancebetween the first and second transmitting devices.

10. A measuring device for measuring cervical dilation comprising:

a. a miniature magnetic device producing a magnetic field, said devicehaving attachment means to attach said device to the wall of saidcervix;

b. a portable moving coil device placeable against the intensity of thecurrent induced in said coil.

1. An electromagnetic device for measuring cervical dilation comprising:a. a first miniature induction coil having a resonant frequency betweenabout 50 and 1000 KCS, said first coil having means to attach said coilto the cervix of a prospective mother, b. a second miniature coil havinga resonant frequency substantially the same as said first coil, saidsecond having means to attach said coil to the cervix of a prospectivemother, c. calibrated power supply means producing an oscillatingcurrent of a frequency substantially matching the resonant frequency ofsaid first miniature induction coil connected to said first miniatureinduction coil to provide predetermined amounts of induced energy insaid second coil at predetermined distances from said first coil, d.translation means interconnected with said second coil to translate theintensity of voltage induced in said coil into a visible displaylinearly proportional to the distance separating said first and secondcoils.
 2. The measuring device of claim 1 wherein the power supply meansprovides a low voltage, alternating current.
 3. The measuring device ofclaim 2 wherein the power supply means provides an alternating currentof less than about 25 volts.
 4. The measuring device of claim 2 whereinthe power supply means provides an alternating current of less thanabout 100 milliwatts.
 5. The measuring device of claim 1 wherein saidtranslation means comprises a peak follower interconnected with saidsecond coil, a log amplifier interconnected with said peak follower, ananti-log amplifier interconnected with said log amplifier and a visualdisplay device for converting an electrical signal into a visualdisplay.
 6. The measuring device of claim 1 wherein the induction coilshave a high ''''Q'''' and a narrow frequency band pass.
 7. The measuringdevice of claim 6 wherein the power supply means provides an oscillatingcurrent at a power of less than about 100 milliwatts, a voltage of lessthan about 25 volts and at a frequency within the band pass range ofsaid coils.
 8. The measuring device of claim 1 wherein each inductioncoil has a maximum dimension of about one-half inch.
 9. A measuringdevice for measuring cervical dilation comprising: a. first miniaturesignal transmitting device having attachment means so said device can beattached to one side Of the cervix, said transmitting device generatinga signal of a substantially constant frequency; b. a second miniaturesignal transmitting device having attachment means so said device can beattached to the opposite side of said cervix from said firsttransmitting device, said second transmitting device generating a signalwhich has a substantially constant frequency different from thefrequency of the first transmitting device; c. a remote receiving unitwhich receives an interference frequency transmitted from saidtransmitting device; d. translation means for receiving saidinterference frequency from said receiving device and translating sameto provide a visible display of the interference frequency received bythe receiving device, said translation means including a visual displaydevice calibrated to display said interference frequency proportionallyto the distance between the first and second transmitting devices.
 10. Ameasuring device for measuring cervical dilation comprising: a. aminiature magnetic device producing a magnetic field, said device havingattachment means to attach said device to the wall of said cervix; b. aportable moving coil device placeable against the cervical wall oppositesaid miniature magnetic device having a moveable coil therein; c.reciprocating means within said moving coil device interacting with saidmoveable coil to reciprocate said coil; d. translation meansinterconnected with said coil for receiving the alternating current fromsaid coil and translating same to provide a visible display of theintensity of the current induced in said coil.